Fusing apparatus



March 11, 1969 H. E. HULL ETAL FUSING APPARATUS Filed Oct. 3, 1966 INVENTORS HENRY E. HULL HAROLD E.'TRUMBULL BY GORDON G.ZEIDMAN FIG. 4

A TTORNE) United States Patent 4 Claims This invention relates to a fusing apparatus for affixing a powder image permanently onto a support surface on which it has been formed, such as, a xerographically formed image.

It is important in fusing powder images to cause the powder to soften and become adhesive without deleteriously affecting the image support, which is usually paper, by burning or scorching. To fuse images formed of powdered resins now commonly used in xerography as described, for example, in U.S. Reissue Patent No. 25,136, it is necessary to heat the powder and support to a relatively high temperature, at times approximately 325 F. It is undesirable, however, to raise the temperature of the paper higher than about 375 F. because of the tendency of paper to discolor at such elevated temperatures. As can readily be appreciated this imposes rather exacting temperature control requirements on the fusing device.

Still other requirements are that the fusing apparatus provide uniform and rapid heat transfer to the support material being heated, that it have relatively low power consumption when left on for extended periods of time when it is maintained in the standby condition, and that it have a relatively brief warm-up period for machine operation.

Most commercial machines that embody the principles of xerography fuse the powder image by one or more electrically energized coils in different arrangements. Normally, the ambient temperature is controlled by a thermostat which in turn regulates the power supply to these coils. These heat fusers are not entirely satisfactory because they require long warm-up periods and have limited efiiciency due to frequent changes in the load conditions.

Now in accordance with the instant invention, there is provided a novel heat fusing apparatus that meets the above requirements and is considerably more thermally eificient than the existing fusers. Generally speaking, the fusing apparatus comprises an oven chamber providing radiant heat on both sides of the paper support to achieve rapid uniform heating thereof and also contains a displaceable wall responsive to the oven temperature to effect selective heating.

It is therefore an object of this invention to improve heat fusing apparatus for aflixing a resinous material onto asupport base. I

It is another object of the invention to incorporate flexibility and thermal efficiency in heat fusing apparatus greater than heretofore.

It is a further object of the invention to render radiant fixing apparatus capable of uniformly fusing powder images on large surface areas of a support material without charring or otherwise deleteriously affecting the support material.

It is a still further object of the invention to adapt a heating fusing apparatus for utilization in an automatic xerographic reproduction machine.

The novel features of the invention, as well as additional objects and advantages thereof, will be understood more fully from the following description when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic representation of a xerographic dice machine utilizing the fusing apparatus according to the present invention;

FIGS. 2, 3 and 4 are end views with parts in section illustrating different embodiments for displacement of the top wall member of the fusing apparatusgand FIG. 5 is a side view of the lift apparatus illustrated in FIG. 4. I

As in all xerographic systems, a radiation light image of copy to be reproduced is projected onto the sensitized surface of a charged xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is usually developed with an oppositely charged developing material to form a xerographic powder image, corresponding to the latent image, of the plate surface. The powder image is then electrostatically transferred to a suitable support surface on which it is fused as by the fusing apparatus of the present invention so that the powder image is permanently affixed to the support surface.

Referring now to FIGURE 1 there is shown the various components of a xerographic system for which the fusing apparatus of the invention may be utilized in schematic fashion. A document to be reproduced is placed on a support tray 10 from which it is fed onto a transport mechanism generally designated 11. Suitable drive means are provided for the transport mechanism from motor 12 to endless belt 13 whereby the document is moved past the optical axis of a projection lens assembly 14 that is illuminated by a projection lamp LM P-l. The image of the copy is reflected by mirror 15 through an adjustable objective lens 15 and then reflected by mirror 17 downwardly through a variable aperture assembly 18 and onto the surface of a xerographic plate in the form of a drum 19.

Xerographic drum 19 includes a cylindrical member mounted in suitable bearings in the frame of the machine and is driven in a clockwise direction by a motor 24 at a constant rate that is proportional to the transport rate of the document whereby the peripheral rate of the drum surface is identical to the rate of movement of the reflected light image. The drum surface comprises a layer of photoconductive insulating material on a conductive backing that is sensitized prior to exposure by means of a corona generating device 25 that is energized from a suitable high potential source.

Exposure of the drum to the light discharges the photoconductive layer in the areas struck by light whereby there remains on the drum a latent electrostatic image in image configuration corresponding to the light image projected from the document. As the drum surface continuies its movement, the electrostatic latent image passes through a developing station 26, in which a two-component developing material 27, which may, for example, be of a type disclosed in U.S. Reissue Patent No. 25,136'is cascaded over the drum surface by means of a developing apparatus 28.

In the developing apparatus, developing material is carried upwardly by conveyor 29 being driven by a suitable drive means from motor 30 and is released onto chute luminated by a lamp LMP-2 whereby residual charges on the non-image areas of the drum surfaceare completely discharged. Thereafter, the powder image passes through an image transfer station 42 at which the powder image is electrostatically transferred to a support 43 by means of a second corona generating device 44, also energized from a suitable potential source.

The support surface to which the powder image is transferred may be of any convenient type, such as paper, that is obtained from a supply roll 45 and is fed over guide rolls 46 and 47 and over suitable tensioning rolls being directed into surface contact with the drum in the immediate vicinity of transfer corona generating device 44.

After transfer, the support surface is separated from the drum surface and is guided through the fusing apparatus of the invention, designated 48, to be described in detail below. Thereafter the support surface is fed over a further system of guide and tensioning rolls and onto a take-up roll 52 that is driven by a motor 53. It should be understood that cut sheets may be used instead of continuous support 43 without detracting from the invention.

After separation of the support surface from the drum, a corona generating device 54 directs an electrostatic charge to residual powder on the drum surface which charge is usually of opposite polarity as used originally for charging. Next, the drum surface is passed through a cleaning station 55 at which its surface is brushed by cleaning brush assembly 56, rotated by a motor 57, whereby residual developing material remaining on the drum is removed. Thereafter, the drum surface passes through a second discharge station 58 where it is illuminated by a fluorescent lamp LMP-3, whereby the entire surface in this region is completely flooded with light to remove any electrostatic charge that may remain thereon.

Suitable light traps are provided in the system to prevent any light rays from reaching the drum surface, other than the projected image, during the period of drum travel immediately prior to sensitization by corona generating device 25 until after the drum surface is completely passed through the developing station 26.

In accordance with the present invention, the fusing apparatus 48 comprises a lower housing 62 containing a chamber 64 and a top wall member 66 between which the support material 43 carrying unfused toner images is advanced. Disposed within chamber 64 is a conventional resistance element 68 for irradiating infrared radia. tion in a manner known by those skilled in the art. The interior wall 70 of chamber 64 and top wall member 66 are made from polished stainless steel or other suitable material to serve as reflectors whereby radiant heat energy emitted from the resistance element can be directed toward both sides of the support material or sheet 43. Wall 70 of chamber 64 may have any suitable shape for efficient reflection such as a parabola, as shown, or alternatively adjacent walls containing, for example, a right angle. Resistance element 68 may be open or insulated, as shown, by a suitable heat sheath 69. It has been found that a seven gram resistance element insulated in a ruby Vycord sheath and having a diameter ranging from 9-15 millimeters works well when support 43 is moving at about 1.5 to 2.5 inches per second and is spaced about half an inch from the resistance element supplied with about 350 watts.

Top wall member 66 is arranged to be displaceable in a direction perpendicular to the path of the support 43 as shown by the arrows in a manner to be described to provide a controlled fusing temperature thereby efi'ecting selective fusing of the powder image on the support 43. During stand-by operation, top wall member 68 rests on or is closely adjacent to the bottom housing 62 and, in effect, forms a closed heating oven which can be maintained at substantially reduced power due to the relatively high thermal efficiency within the closed chamber or oven. This latter condition enables relatively fast warm-up periods which may be utilized to shorten the time between stand-by condition and machine operation.

Referring now to FIGURES 2-4 wherein like numerals identify like elements, there is shown different embodiments of the structure for controlling the spacing of the top wall member 66 relative to bottom housing 62. In the embodiment of FIG. 2, the top wall member 66 comprises a plenum chamber 76 containing a plurality of apertures opening to the exterior. Connected to the top of the plenum chamber 76 is a conduit 78 providing communication between plenum chamber 76 and a variable speed forced draft blower 79. The pressurized air in plenum chamber 76 escapes to the atmosphere through aperture 75 thereby forming an air cushion to raise wall member 66 which is supported in guides not shown. By regulating the pressurized air cushion beneath top wall member 66, spacing from the image bearing support 43 is varied and hence the fusing temperature controlled. A rheostat regulates the speed of blower 79 in response to a thermostat 84 preset to a desired fusing temperature. When the fusing temperature changes, the speed of blower 79 is varied bythe setting of rheostat 80 according to the preset condition on thermostat 84. During stand-by operation the power to the resistance element 68 is reduced but the oven temperature remains the same due to the preset temperature on thermostat 84. If desired during stand-by operation the thermostat 84 may be reset to a lowered temperature condition.

In the embodiment of FIGURE 3 top wall member 66 is supported by a plurality of bimetallic strips 85 which are responsive to the ambient temperature. As the temperature changes the spacing of the top wall member it is similarly varied by the flexing of the bimetallic strips in response thereto.

FIGURES 4 and 5 show still another embodiment for controlling the temperature within fusing apparatus 48. Top wall member 66 has a guide member through which is received fixed post member 91 thereby permitting vertical movement of the wall member relative thereto. A chain 92 pinned to sprocket 93 at one end and guide member 90 at the opposite endv raises and lowers top wall member 66 upon rotation of drive shaft 95 in the counterclockwise and clockwise directions, respectively. Reversible motor 97 drives the shaft 95 in response to signals received from thermostats 9S and 99 which are preset for a desired high and low temperature range, respectively.

It was found that power consumption is substantially less with the fusing apparatus according to the present invention by comparison with prior art fusing devices operating under analogous operating requirements. This result is believed to stem from the combined heat losses being very low and, hence, the efiiciency of the apparatus is very high. As can readily be appreciated when the fusing apparatus is in the fully closed position, which is representative of the stand-by condition, the power supplied can be substantially reduced with sacrificing a significant reduction in temperature.

By the above descripton there has been disclosed a unique heat fusing apparatus for fixing powder resinous images to a support base on which an image has been loosely formed. The apparatus is highly effective in that softening of the resinous image is achieved by heat radiation from both sides of the support base thereby attaining high uniform temperatures desirable for high quality fusing. At the same time, the thermal efliciency is very high, since heat losses to the ambient air are controllable by displacing the top wall of the fuser chamber relative to the support base. Further, with the displaceable top cover construction the fuser is fully closed during standby operating resulting in shorter warm-up periods at reduced power. Also when the machine is in stand-by operation, there is no likelihood that ambient temperature can rise high enough to deleteriously affect the xerographic drum or other heat senstive materials in the machine.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for fusing a resinous powder image onto a support surface on which the image has been loosely formed comprising in combination:

, (a) support means for advancing a support base containing a loosely adhering resinous powder image on its surface in a predetermined path,

(b) contiguous walls forming a partially enclosed chamber positioned adjacent to the support base path, the interior portion of said chamber being shaped to reflect radiation in a direction toward one surface of the support base,

(c) heater means disposed within said chamber and extending transverse to the support base path and adapted to emit radiation toward one surface of said support base for heating same,

(d) a displaceable wall member positioned opposite said chamber, on the other side of the support base and adapted to reflect radiation received toward the other surface of the support base, said wall member being movable in a direction perpendicular to the support base and defining a substantially enclosed housing with said contiguous walls when in a rest position; and

(e) control means responsive to the fusing temperature for varying the spacing of said movable wall member relative to the supportbase.

2. Apparatus according to claim 1 wherein said movable wall member comprises a plenum chamber containing apertures in the bottom opening to the exterior and said control means includes a variable speed air blower,

et, and electrical circuit means responsive to a high and low temperature range to energize said motor to rotate said sprocket in both the clockwise and counter-clockwise directions depending upon the fusing temperature.

4. Apparatus according to claim 1 wherein said control means comprises a plurality of bimetallic strips supporting said displaceable Wall member, said strips being responsive to the fusing temperature to raise and lower said wall member relative to said support base.

References Cited UNITED STATES PATENTS 2,807,703 9/1957 Roshon 219-388 X 3,053,962 9/1962 Cerasoni et al '95l.7 X 3,275,799 9/1966 Meltzer 2l9342 3,382,360 5/1968 Young et a1 250-- X RICHARD M. WOOD, Primary Examiner.

C. L. ALBRITTON, Assistant Examiner.

US. Cl. X.R. 

1. APPARATUS FOR FUSING A RESINOUS POWDER IMAGE ONTO A SUPPORT SURFACE ON WHICH THE IMAGE HAS BEEN LOOSELY FORMED COMPRISING IN COMBINATION: (A) SUPPORT MEANS FOR ADVANCING A SUPPORT BASE CONTAINING A LOOSELY ADHERING RESINOUS POWDER IMAGE ON ITS SURFACE IN A PREDETERMINED PATH, (B) CONTIGUOUS WALLS FORMING A PARTIALLY ESCLOSED CHAMBER POSITIONED ADJACENT TO THE SUPPORT BASE PATH, THE INTERIOR PORTION OF SAID CHAMBER BEING SHAPED TO REFLECT RADIATION IN A DIRECTION TOWARD ONE SURFACE OF THE SUPPORT BASE, (C) HEATER MEANS DISPOSED WITHIN SAID CHAMBER AND EXTENDING TRANSVERSE TO THE SUPPORT BASE PATH AND ADAPTED TO EMIT RADIATION TOWARD ONE SURFACE OF SAID SUPPORT BASE FOR HEATING SAME, (D)A DISPLACEABLE WALL MEMBER POSITIONED OPPOSITE SAID CHAMBER, ON THE OTHER SIDE OF THE SUPPORT BASE AND ADAPTED TO REFLECT RADIATION RECEIVED TOWARD THE OTHER SURFACE OF THE SUPPORT BASE, SAID WALL MEMBER BEING MOVABLE IN A DIRECTION PERPENDICULAR TO THE SUPPORT BASE AND DEFINING A SUBSTANTIALLY ENCLOSED HOUSING WITH SAID CONTIGUOUS WALLS WHEN IN A REST POSITION; AND (E) CONTROL MEANS RESPONSIVE TO THE FUSING TEMPERATURE FOR VARYING THE SPACING OF SAID MOVABLE WALL MEMBER RELATIVE TO THE SUPPORT BASE. 